If your Mac freezes, apps quit for no reason, files won't copy, or an external drive keeps ejecting itself, the first free thing to try is Disk Utility First Aid. It checks a drive's directory and formatting for errors and repairs what it safely can — no download, no shop visit, and nothing is erased when it works. Here's exactly how to run it the right way.
What First Aid actually does (and doesn't)
First Aid runs a filesystem check (the modern equivalent of the old fsck and "Repair Disk") on a volume. It verifies that the drive's catalog — the map of where every file lives — matches what's actually on the disk, and fixes mismatches, orphaned entries, and minor corruption. It is non-destructive: a normal First Aid pass does not delete your files. What it cannot do is fix a drive that is physically failing — for that, the only real fix is backup and replacement (covered at the bottom).
How to run First Aid from the desktop (any regular volume or external drive)
- Open Disk Utility — press Command-Space, type "Disk Utility", and hit Return (or find it in Applications > Utilities).
- In the sidebar, click the volume you want to check (for your main drive that's usually "Macintosh HD"; for an external, click its named volume).
- Click the First Aid button in the toolbar, then click Run, then Continue.
- Wait. First Aid usually takes 2–10 minutes depending on drive size and how much is stored. When it finishes you'll see a green "Operation successful" — click Done.
If you want the full report, click the small Show Details triangle while it runs. Green text is normal; a red line means it found (and usually repaired) a problem.
Repair the whole disk, not just the volume: View > Show All Devices
By default Disk Utility hides the lower layers of the drive. On modern APFS Macs a single physical disk contains a container, which holds one or more volumes. Errors can live at any layer, so repair from the bottom up:
- In Disk Utility's menu bar, choose View > Show All Devices.
- The sidebar now shows the physical disk at the top (e.g. "APPLE SSD…"), the container below it, and your volumes nested inside.
- Run First Aid from the bottom up: first the volume, then the container, then the physical disk. Repairing the bottom layer can clear errors the volume check couldn't reach.
Repairing the startup disk: run First Aid from Recovery
You can't fully repair the disk macOS is currently running from while it's booted — the drive is in use. To repair the boot disk, run First Aid from macOS Recovery instead, where the system drive is unmounted and fully repairable. The steps to get into Recovery differ by chip, and we cover them in full here: How to use MacBook Recovery Mode. Once you're in Recovery, choose Disk Utility, then run First Aid on Macintosh HD (again, use Show All Devices and go bottom-up).
What to do if First Aid fails
Sometimes First Aid stops with a red error like "The volume … could not be verified completely" or "First Aid found corruption that needs to be repaired… run First Aid on the disk and try again." Work through this order:
- Run it again from Recovery. A repair that fails on a mounted, in-use disk often succeeds from Recovery where the volume is unmounted.
- Repair the container and physical disk too (Show All Devices, bottom-up) — a volume can't be fixed if the container beneath it is damaged.
- Back up immediately. If it still fails, treat the drive as untrustworthy. Copy your important files off now, before doing anything else — a failing drive can get worse each time it's powered on.
- Erase and reinstall. With a backup safe, erase the volume in Disk Utility and reinstall macOS. This clears filesystem corruption that First Aid alone couldn't repair.
- If errors return after a clean erase, the drive hardware itself is failing. On a Mac with soldered storage that usually means end of life for that machine.
First Aid on an external drive that won't show up
If an external drive doesn't mount, open Disk Utility and choose View > Show All Devices — a drive that won't mount often still appears (greyed out) as a physical device. Select it and run First Aid; if it repairs, the volume may remount. If it can't be repaired or doesn't appear at all, work through our external drive not showing up guide before assuming the drive is dead.
Related guides
- How to use MacBook Recovery Mode — repair the boot disk or reinstall macOS
- How to partition a Mac drive — APFS volumes vs. partitions, done safely
- Mac storage full? — reclaim space without erasing anything
- Mac running slow? — the fixes that actually help
Frequently Asked Questions
Does running First Aid erase my Mac?
No. A normal First Aid pass checks and repairs the drive's directory without deleting your files. Erasing only happens if you manually choose Erase after First Aid can't repair the disk — and even then you'd restore from your backup.
How long does First Aid take?
Usually 2–10 minutes for a typical drive. Very full or very large drives can take longer. If it appears frozen for an hour with no progress, force-quit, restart, and try again from Recovery.
What does "First Aid found corruption that needs to be repaired" mean?
It found directory errors and is repairing them — let it finish. If it then says it couldn't repair completely, re-run it from Recovery and repair the container and physical disk too (View > Show All Devices).
Can First Aid fix a physically failing SSD or hard drive?
No. First Aid fixes filesystem/software errors, not hardware. If errors keep returning even after a clean erase and reinstall, the drive itself is failing.
Do you buy Macs with drive or storage problems?
Yes — a Mac with a failing drive still has trade-in value, and replacing it doesn't have to cost new-Mac money.
Fixed it — or found something bigger?
If First Aid got your drive healthy again, you're done — no charge and no shop visit. If it uncovered a failing drive instead, you have two easy paths: get a quote for the machine as-is, or replace it with a warrantied refurb from our Apple clearance lineup. Either way, Rick on chat can walk you through it in about two minutes.